Concrete is weak in tension and requires some form of reinforcement. Steel rebar is often used in order to cater for tensile and compressive forces. Millard et al. (2009) suggests that when concrete is subject to blast forces, failure occurs at the surface of a concrete wall, and the presence of conventional steel reinforcement will generally not prevent the wall from material spalling. An explosion near to a concrete wall causes a high speed pressure wave to load the front face of the wall (Millard et al., 2009). A small proportion of this energy will be reflected back, while a significant proportion of the energy will travel through the wall as a compressive stress wave (Millard et al., 2009). The reflection of the compressive stress wave within the concrete causes a tension rebound from the back face; it is this tension rebound that can cause the back face to spall (Millard et al., 2009). Impact by a high speed point load, such as a bullet, has similarities with a small standoff blast (Millard et al., 2009). Back face spall is an important consideration for protecting the public against fragmentation due to impact on concrete structures and this article investigates fibre concrete performance. Synthetic fibres may offer additional protection with regard to energy absorption; the fibres are dispersed throughout the mix during batching and this can provide additional toughness of the concrete, especially between the rebar spacing. This research investigates the use of Type 1 micro synthetic fibres, Type 2 macro synthetic fibres and steel fibres used as reinforcement in concrete samples when subject to various forces. The purpose of this test programme was to compare each of these fibre types against a plain concrete control sample. The tests subjected the specimens to flexural bending, single point loading impact and shot gun fire. The parameters of the test were: compressive strength, flexural strength including load deflection analysis, energy absorption and impact resistance using a drop hammer, and a shotgun fire performance test. The test specimens were modelled using Finite Element Analysis (FEA) in order to predict the damage on the slabs from the shotgun fire performance test and inform the apriori slab design. The overall test programme is displayed in Figure 1. Although many tests were carried out, the shotgun test is the main focus of this article.
|Publication status||Published - Dec 2015|